Traditionally, radio frequency (“RF”) communications systems, such as those interacting with wireless local area networks (“WLANs”), arrange their constituent elements in one of two configurations. In a first approach, RF radio circuits are collocated with base band circuits, both of which are typically integrated as part of a chip set that includes, for example, medium access control (“MAC”) layer circuits and/or a central processing unit (“CPU”). In a second approach, RF radio circuits are located remotely from the base band circuits. Generally, radio circuits include receiver circuits and/or transmitter circuits, or both, and base band circuits include modulating and demodulating circuits.
FIG. 1A shows a conventional communications system 100 that is representative of the first approach. System 100 arranges RF radio circuits 108 and base band subsystem 110, which includes base band circuits, at or near the same location on a common substrate 106, such as a printed circuit board (“PCB”) or a single chip application-specific integrated circuit (“ASIC”). A crystal oscillator (not shown) is generally used to generate fixed clock signals to exchange digitized communications data between RF radio circuits 108 and base band subsystem 110. Cable 104 couples system 100 with an antenna 102 for receiving and transmitting RF signals. Importantly, the physical structure of cable 104 is designed contain emissions that might give rise to EMI. In this arrangement, antenna 102 resides at a location at some distance, “d,” from RF radio circuits 108. To illustrate this arrangement, consider that a mobile computing device implements system 100 such that RF radio circuits 108 and base band subsystem 110 are both located below or near a keypad or key board, whereas and antenna 102 is located behind or near the top of a display (not shown). FIG. 1B shows another conventional communications system 150 that is representative of the second approach. But in this arrangement, RF radio circuits 108 are disposed adjacent antenna 102 at distance “d” from base band subsystem 110. Regardless, both approaches implement cable 104 as either a coaxial cable or some other kind of shielded cable to quell the effects of EMI.
While functional, both above-described approaches have several drawbacks. For example, cable 104 is implemented as a specialized coaxial cable to reduce deleterious EMI arising from clocking data with a fixed clock frequency. That is, cable 104 is usually a mini-coaxial or a micro-coaxial cable, both of which are relatively costly solutions to minimize EMI radiation. These cables are relatively complex to manufacture. As cable 104 is frequently used in mobile computing devices, such as in lap top computers, it must have a small cross-sectional area to pass through hinged mechanisms and to save space while providing sufficient EMI shielding. Further, mini-coaxial and micro-coaxial cables usually have relatively high cable losses at high frequencies and at relatively long lengths when data signals are transmitted as analog signals rather than digital signals.
In view of the foregoing, it would be desirable to minimize the above-mentioned drawbacks by providing an antenna system and a high-speed digital data link for placing radio circuits remotely from a base band circuit in an RF communications system.